The present invention resides in a vent valve that is used in fuel tanks and the like to permit air to pass freely in or out of the tank without losing the confined liquid. More particularly, the present invention is concerned with a vent valve that in addition to the venting function also relieves excessive internal pressure when other vent valves would normally remain closed.
Fuel vent valves of the prior art have certain inherent problems. Pivoted or overhung valves used in aircraft are attitude sensitive, and can leak large amounts of fuel under certain combinations of pitch, roll and valve orientation within the craft. Direct-acting valves have a tendency to be pulled closed at high fueling rates due to rapidly escaping air and often do not reopen until internal tank pressures have dropped considerably below atmospheric pressure. Both types of prior art valves are used with a separate relief valve to bleed off excess pressures generated by thermal expansion within the tank after the tanks have been topped off, or to protect the tanks and surrounding structure against excess pressures when a component in the automatic fuel shutoff equipment fails and the tank is overfilled. A further problem that arises in tanks having both vent and relief valves is that the relief valve cannot discriminate between fuel and air and may spew out fuel rather than air under certain conditions.
It is, accordingly, a general object of the present invention to provide a vent valve that integrates relief valve functions and which is self-compensating to provide greater pressure relief with greater internal tank pressures. It is a further object of the invention to provide a vent valve that is stable in its transition from a venting to a closed position and which is highly sensitive to internal tank pressures.